fix: add None guard for params in get_balance_allowance and update_balance_allowance

[zyaiire]

Summary

Fixes #306

Adds a None guard to get_balance_allowance and update_balance_allowance to prevent an opaque AttributeError when called without the params argument.

Description

Both methods declare params: BalanceAllowanceParams = None as optional but immediately access params.signature_type without a None check. This causes an opaque AttributeError: 'NoneType' object has no attribute 'signature_type' when called without params.

This adds a guard after self.assert_level_2_auth() in each method that raises a clear ValueError("params is required for ...") before accessing any attributes. The guard is placed after the auth check to maintain consistent error semantics - unauthenticated callers always get the auth error first, matching the behavior of every other method in the class.

No change to method signatures or behaviour for callers who pass params correctly.

Changes

• Added None check with clear ValueError in get_balance_allowance (after auth check)
• Added None check with clear ValueError in update_balance_allowance (after auth check)
• Added test file tests/test_balance_allowance.py covering both cases

Testing

• pytest tests/test_balance_allowance.py - verifies both methods raise ValueError when called without params
• Existing test suite unchanged - no regressions for callers passing valid params

Note

This addresses the review feedback on #307 (the None guard should be placed after assert_level_2_auth() to maintain consistent error ordering).

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Note

Low Risk
Low risk: adds explicit argument validation to two client methods and a small unit test, without changing request behavior for valid callers.

Overview
Adds explicit None guards to ClobClient.get_balance_allowance and ClobClient.update_balance_allowance, raising a clear ValueError instead of failing later with an AttributeError when called without params.

Introduces tests/test_balance_allowance.py to assert both methods require params and error deterministically.

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